The present invention relates to a catalyst for producing lower fatty acid esters, through a reaction between a lower aliphatic carboxylic acid and a lower olefin; a process for producing the catalyst; and a process for producing lower fatty acid esters by using the catalyst.
A reaction between a lower olefin and a lower aliphatic carboxylic acid in the presence of an acidic catalyst is known to yield the corresponding lower fatty acid ester. In addition, a heteropoly acid and a salt thereof are known to serve as an effective catalyst for the reaction. For example, Japanese Unexamined Patent Publications (Kokai) No. 4-139148, No. 4-139149, No. 5-65248, No. 5-163200, No. 5-170699, No. 5-255185, No. 5-294894, No. 6-72951, and No. 9-118647 disclose conventional techniques in relation to the above process and catalyst.
In these techniques, catalyst components and reaction conditions are elaborated from various aspects, and lower fatty acid esters can be produced with a comparatively high yield. However, nowadays, there is a demand for a catalyst having higher performance and a higher activity per unit time.
Among these publications, Japanese Unexamined Patent Publications (Kokai) No. 5-294894 and No. 9-118647 disclose a so-called supported catalyst in which a heteropoly acid and/or a salt thereof serving as an active component are held on a carrier formed of a porous substance such as silica gel.
In general, the catalytic properties of a produced supported catalyst depend on the type and properties of the carrier for supporting the catalyst component. In addition, the catalyst performance, such as catalytic activity or selectivity of a target product during reaction, varies depending on the properties of the produced supported catalyst.
The aforementioned Japanese Unexamined Patent Publications (Kokai) No. 5-294894 and No. 9-118647 fail to provide detailed discussion of a carrier, and furthermore, do not disclose the catalytic performance of a prepared supported catalyst, particularly performance attributed to the properties of the carrier.
In view of the foregoing, an object of the present invention is to provide a catalyst having higher catalytic activity in a process for producing a lower fatty acid ester through esterification of a lower olefin with a lower aliphatic carboxylic acid in the presence of a catalyst wherein at least one compound selected from heteropoly acids and salts thereof is caused to be held on a carrier. Another object of the invention is to provide a process for producing the catalyst. Still another object of the invention is to provide a process for producing a lower fatty acid ester by using the catalyst.
The present inventors have conducted intensive studies to obtain a catalyst which has high performance and is useful for producing lower fatty acid esters through reaction of a lower olefin and a lower aliphatic carboxylic acid.
Thus, the present inventors have found that the catalytic activity of a supported catalyst used in the above reaction containing a heteropoly acid and/or a salt thereof can be improved remarkably when the specific surface area of the catalyst, as measured by a BET method, falls within a specific range. The present invention has been accomplished on the basis of this finding.
Accordingly, the present invention (I) provides a catalyst for producing a lower fatty acid ester which catalyst contains at least one compound selected from heteropoly acids and salts thereof, which compound is caused to be held on a carrier and which catalyst is used in a process for producing a lower fatty acid ester through esterification of a lower aliphatic carboxylic acid with a lower olefin, wherein the specific surface area of the catalyst, as measured by a BET method, is 65 m2/g-350 m2/g.
The present invention (II) provides a catalyst according to the present invention (I) used for producing a lower fatty acid ester, which catalyst has a specific surface area of the carrier as measured by BET method of 100 m2/g-500 m2/q.
The present invention (III) provides a process for producing the catalyst as recited in the present invention (I) or (II) useful for producing a lower fatty acid ester.
The present invention (IV) provides a process for producing a lower fatty acid ester through esterification of a lower aliphatic carboxylic acid with a lower olefin in the presence of the catalyst as recited in the present invention (I) or (II).
The present invention will now be described in detail.
The catalyst for producing a lower fatty acid ester according to the invention (I) will be described. The invention (I) encompasses a catalyst for producing a lower fatty acid ester, which catalyst contains at least one compound selected from heteropoly acids and salts thereof, which compound is caused to be held on a carrier and which catalyst is used in a process for producing a lower fatty acid ester through esterification of a lower aliphatic carboxylic acid with a lower olefin, wherein the specific surface area of the catalyst, as measured by a BET method, is 65 m2/g-350 m2/g.
The heteropoly acids used in the invention (I) comprise a hetero element and poly elements bonded to oxygen. The hetero element is typically silicon or phosphorus, but is not limited thereto, and can be optionally selected from elements belonging to Groups 1-17 in the periodic table (Nomenclature of Inorganic Chemistry by International Union of Pure and Applied Chemistry, revised edition (1989); the same applies hereinafter).
The hetero element is not particularly limited, and examples thereof include a cupric ion; a divalent ion of beryllium, zinc, cobalt, or nickel; a trivalent ion of boron, aluminum, gallium, iron, cerium, arsenic, antimony, phosphorus, bismuth, chromium, or rhodium; a tetravalent ion of silicon, germanium, tin, titanium, zirconium, vanadium, sulfur, tellurium, manganese, nickel, platinum, thorium, hafnium, cerium, or other rare earth metals; a pentavalent ion of phosphorus, arsenic, vanadium, or antimony; a hexavalent tellurium ion; and a heptavalent iodine ion.
The poly element is not particularly limited, and examples thereof include tungsten, molybdenum, vanadium, niobium, and tantalum.
Such a heteropoly acid is well known as xe2x80x9ca polyoxo anion,xe2x80x9d xe2x80x9ca polyoxo metal salt,xe2x80x9d or xe2x80x9can oxidized metal cluster.xe2x80x9d Some structures of the well-known anions are named after researchers in this field, such as the Keggin structure, the Dawson structure, and the Anderson-Evans-Pearov structure. A heteropoly acid typically has a high molecular weight, e.g., a molecular weight of 700-8500, and also encompasses a dimer complex thereof.
No particular limitation is imposed on the heteropoly-acid salt, and a metal salt or an onium salt may be used so long as a portion of or all hydrogen atoms of the heteropoly-acid are substituted. Non-limitative examples include metal salts of lithium, sodium, potassium, cesium, magnesium, barium, copper, gold, and gallium; and onium salts such as ammonium salts.
A heteropoly acid compound, particularly when in the form of a free acid or a salt, has comparatively high solubility to a polar solvent such as water or a oxygen-containing compound solvent, and the solubility thereof can be controlled by the selection of a suitable counter ion of the salt.